The present invention relates to vaccine compositions for delivery to mucosal surfaces, and to a method of inducing, in a mammal, an immune response to an antigen by delivering the antigen to a mucosal surface of the mammal. More particularly, the present invention relates to vaccine compositions for inoculating a mammal such as a human against picornavirus infection and particularly Hepatitis A infection.
Hepatitis A is an acute disease caused by infection with a small picornavirus closely related to the poliovirus. Infection is spread by the faecal/oral route and consequently the disease in endemic in areas where hygiene and sanitation standards are low. The risk of travellers to developing countries acquiring Hepatitis A is far greater than that of contracting typhoid and cholera (40 and 800 times respectively).
The virus itself is not directly cytopathic. The liver damage resulting from Hepatitis A virus (HAV) infection arises from destruction of virally infected cells by the host""s cytotoxic T-lymphocytes. There is only a single serotype of HAV and infection results in long-term immunity, characteristics that are ideal for developing Hepatitis A prophylaxis. Protection is mediated by neutralising antibodies that prevent entry of hepatitis A virus into hepatocytes. Passive immunisation with purified human serum xcex3-globulin provides short term protection against the disease and until recently this was the only means of preventing hepatitis A.
In recent years, HAV vaccines have been developed but development has focused on inactivated and live attenuated vaccines. Both types of vaccines are prepared from HAV propagated in tissue culture cells. HAV replication is slow and the majority of the virus remains cell associated, and consequently the viral yields are low and relatively commercially unattractive. The problem of low viral yield could be overcome by using recombinant techniques which allow for the production of large quantities of proteins. However, it is important to ensure correct processing and folding of HAV proteins because the known neutralising epitopes are conformationally dependent. It has proved difficult so far to obtain recombinant HAV antigens that elicit appropriate immune responses.
One recombinant HAV antigen that has proved successful in inducing protection against HAV when injected parenterally is the HAV capsid preparation developed by American Biogenetic Sciences. American Biogenetic Sciences have succeeded in producing empty HAV capsids in eucaryotic cells using vaccinia and baculovirus expression vectors. The recombinant capsids are recognised by neutralising monoclonal antibodies, induce protection against HAV in chimpanzees when injected parenterally and are produced in considerably larger quantities than that obtained by conventional means. The HAV capsids are disclosed in International Patent Application WO-A-9301279, the disclosure in which is incorporated herein by reference.
A disadvantage with many vaccination regimens is that it is frequently necessary to administer the vaccine composition by means of injection, a factor which has a potential deterrent effect to many people, particularly when follow-up or booster injections are required to complete a course of treatment. One way of overcoming this problem would be to administer the vaccine composition to the oral or nasal mucosa, but although immunisation by the oral or intranasal route has been explored with certain other antigens, it has been found usually to be less effective in evoking serum antibodies than parenteral immunisation. For example, the article by M. H. Siogren et al, Vaccine, Vol. 10, Suppl. 1, S135-S137, 1992, describes the administration of a live attenuated hepatitis A vaccine by either the oral route or the intramuscular route. Whereas intramuscular administration elicited a good serum antibody response, an antibody response to oral administration was not observed at any dose.
The fact that there are very few mucosal vaccines commercially available indicates that there are problems with developing such vaccines. May non-living soluble antigens, particularly those used traditionally by immunologists, such as ovalbumin (OVA) and Keyhole Limpet Haemocyanin (KLH) are poor mucosal immunogens. Large doses of such antigens are necessary to induce any responses but large doses can also cause tolerance in the individual to subsequent parenteral exposure to antigen, a condition known as Oral Tolerance. Although some microbial components such as the cholera toxin (CT) or E. coli heat labile toxin (LT) or the non-toxic binding portions of these toxins (CT-B and LT-B) have been found to be potent mucosal immunogens eliciting strong secretory and circulating antibodies, the reasons why such molecules are good mucosal immunogens has not been fully elucidated. One property that may be important is the ability of these molecules to bind to mucosal epithelial cells via certain surface receptors, although it has been found in studies by others that there is not necessarily a correlation between the ability of an antigen to bind to eucaryotic cells and its mucosal immunogenicity. In the present case, it is not known, at the molecular or cellular level, how HAV enters the body, nor is it known whether specific receptors are involved.
Thus, as far as we are aware, there is currently no way of predicting with any certainty whether a given antigen will possess good mucosal immunogenicity.
It has now been found that the recombinant empty HAV capsid referred to hereinabove, when administered mucosally, and in particular intranasally, is efficient at inducing serum anti-HAV antibodies. Thus, when the HAV capsid preparation was administered intranasally, following first and second booster doses, seroconversion to anti-HAV was observed in the majority of animals, and this compared favourably with the administration of the antigen in the presence of an alum adjuvant by the subcutaneous route.
Accordingly, in a first aspect, the invention provides the use of Hepatitis A virus capsid, or mucosally immunogenic fragments or epitopes thereof, for the manufacture of a mucosal vaccine composition for administration to a mucosal""surface of a patient to induce the production of serum Immunoglobulin G antibody against Hepatitis A virus.
In a second aspect, the invention provides a vaccine composition for application to a mucosal surface, the composition comprising Hepatitis A virus capsid, or a mucosally immunogenic fragment or epitope thereof, and a pharmaceutically acceptable carrier.
In a still further aspect of the invention, there is provided a method of inducing the production of serum Immunoglobulin G antibody against Hepatitis A virus in a host such as a mammal (eg. human), which method comprises administering an effective amount of a Hepatitis A virus capsid antigen, or a mucosally immunogenic fragment or epitope thereof, directly to a mucosal surface in the host.
The mucosal delivery compositions of the present invention can be formulated, for example, for delivery to one or more of the oral, gastro intestinal, and respiratory (eg. nasal and bronchial) mucosa.
Where the composition is intended for delivery to the respiratory (eg. nasal or bronchial) mucosa, typically it is formulated as an aqueous solution for administration as an aerosol or nasal drops, or as a dry powder eg. for inhalation.
Compositions for administration as nasal drops may contain one or more excipients of the type usually included in such compositions, for example, preservatives, viscosity adjusting agents, tonicity adjusting agents, buffering agents and the like. The vaccine compositions of the present invention may also take the form of compositions intended to deliver the antigen to mucosal surfaces in the gastro intestinal tract. Such compositions can be provided with means for preventing degradation of the antigens by the gastric juices, for example by encasing the vaccine preparation in a capsule within a protective matrix or coating of known type.
The quantity of Hepatitis virus A capsid administered to the patient typically is selected such that it is non-toxic to the patient at concentrations employed to elicit an immune response. For example, the concentration of capsid administered may lie in the range 0.1 mg to 100 mg per kg/host.
The invention will now be illustrated in more detail by reference to the specific embodiments described in the following examples, and illustrated in the accompanying drawings. The examples are intended to be purely illustrative of the invention and are not intended to limit its scope in any way.